An aromatic carbonates is important as a raw material for the production of aromatic polycarbonate which is the most widely used engineering plastic, without using toxic phosgene. As a process for producing an aromatic carbonate, a process of reacting an aromatic monohydroxy compound with phosgene has been known from long ago, and has also been the subject of a variety of studies in recent years. However, this process has the problem of using phosgene, and in addition chlorinated impurities that are difficult to separate out are present in the aromatic carbonate produced using this process, and hence the aromatic carbonate cannot be used as the raw material for the production of the aromatic polycarbonate. Because such chlorinated impurities markedly inhibit the polymerization reaction in the transesterification method which is carried out in the presence of an extremely small amount of a basic catalyst; for example, even if such chlorinated impurities are present in an amount of only 1 ppm, the polymerization hardly proceeds at all. To make the aromatic carbonate capable of being used as the raw material of polycarbonate of the transesterification method, troublesome multi-stage separation/purification processes such as enough washing with a dilute aqueous alkaline solution and hot water, oil/water separation, distillation and so on are thus required. Furthermore, the yield of the aromatic carbonate decreases due to hydrolysis loss during this separation/purification processes. Therefore, there are many problems in carrying out this method economically on an industrial scale.
On the other hand, a process for producing aromatic carbonates through transesterification reactions between a dialkyl carbonate and an aromatic monohydroxy compound is also known. However, such transesterification reactions are all equilibrium reactions. Since the equilibriums are biased extremely toward the original system and the reaction rates are slow, and hence there have been many difficulties in producing aromatic carbonates industrially in large amounts using this method. Several proposals have been made to improve on the above difficulties, but most of these have related to development of a catalyst to increase the reaction rate. Many metal compounds have been proposed as catalysts for this type of transesterification reaction. For example, Lewis acids such as a transition metal halide and Lewis acid-forming compounds (see Patent Documents 1: Japanese Patent Application Laid-Open No. 51-105032, Japanese Patent Application Laid-Open No. 56-123948, Japanese Patent Application Laid-Open No. 56-123949 (corresponding to West German Patent Application No. 2528412, British Patent No. 1499530, and U.S. Pat. No. 4,182,726), Japanese Patent Application Laid-Open No. 51-75044 (corresponding to West German Patent Application No. 2552907, and U.S. Pat. No. 4,045,464)), tin compounds such as an organo-tin alkoxide and an organo-tin oxides (see Patent Documents 2: Japanese Patent Application Laid-Open No. 54-48733 (corresponding to West German Patent Application No. 2736062), Japanese Patent Application Laid-Open No. 54-63023, Japanese Patent Application Laid-Open No. 60-169444 (corresponding to U.S. Pat. No. 4,554,110), Japanese Patent Application Laid-Open No. 60-169445 (corresponding to U.S. Pat. No. 4,552,704), Japanese Patent Application Laid-Open No. 62-277345, Japanese Patent Application Laid-Open No. 1-265063, Japanese Patent Application Laid-Open No. 60-169444 (corresponding to U.S. Pat. No. 4,554,110), Japanese Patent Application Laid-Open No. 60-169445 (corresponding to U.S. Pat. No. 4,552,704), Japanese Patent Application Laid-Open No. 62-277345, Japanese Patent Application Laid-Open No. 1-265063), salts and alkoxides of alkali metals and alkaline earth metals (see Patent Document 3: Japanese Patent Application Laid-Open No. 57-176932), lead compounds (see Patent Documents 4: Japanese Patent Application Laid-Open No. 57-176932, Japanese Patent Application Laid-Open No. 1-93560), complexes of metals such as copper, iron and zirconium (see Patent Document 5: Japanese Patent Application Laid-Open No. 57-183745), titanic acid esters (see Patent Documents 6: Japanese Patent Application Laid-Open No. 58-185536 (corresponding to U.S. Pat. No. 4,410,464), Japanese Patent Application Laid-Open No. 1-265062), mixtures of a Lewis acid and a protonic acid (see Patent Document 7: Japanese Patent Application Laid-Open No. 60-173016 (corresponding to U.S. Pat. No. 4,609,501)), compounds of Sc, Mo, Mn, Bi, Te or the like (see Patent Document 8: Japanese Patent Application Laid-Open No. 1-265064), ferric acetate (see Patent Document 9: Japanese Patent Application Laid-Open No. 61-172852), and so on have been proposed. However, the problem of the disadvantageous equilibrium cannot be solved merely by developing the catalyst, and hence there are very many issues to be solved including the reaction system in order to provide a process for the industrial production aiming for mass production.
Attempts have also been made to devise a reaction system so as to shift the equilibrium toward the product system as much as possible, and thus improve the yield of the aromatic carbonates. For example, for the reaction between dimethyl carbonate and phenol, there have been proposed a method in which by-produced methanol is distilled off by azeotropy together with an azeotrope-forming agent (see Patent Document 10: Japanese Patent Application Laid-Open No. 54-48732 (corresponding to West German Patent Application No; 736063, and U.S. Pat. No. 4,252,737)), and a method in which the methanol produced as the by-product is removed by being adsorbed onto a molecular sieve (see Patent Document 11: Japanese Patent Application Laid-Open No. 58-185536 (corresponding to U.S. Pat. No. 410,464)). Moreover, a method has also been proposed in which, using an apparatus in which a distillation column is provided on top of a reactor, an alcohol produced as the by-product in the reaction is separated off from the reaction mixture, and at the same time unreacted starting material that evaporates is separated off by distillation (see Patent Documents 12: examples in Japanese Patent Application Laid-Open No. 56-123948 (corresponding to U.S. Pat. No. 4,182,726), examples in Japanese Patent Application Laid-Open No. 56-25138, examples in Japanese Patent Application Laid-Open No. 60-169444 (corresponding to U.S. Pat. No. 4,554,110), examples in Japanese Patent Application Laid-Open No. 60-169445 (corresponding to U.S. Pat. No. 4,552,704), examples in Japanese Patent Application Laid-Open No. 60-173016 (corresponding to U.S. Pat. No. 4,609,501), examples in Japanese Patent Application Laid-Open No. 61-172852, examples in Japanese Patent Application Laid-Open No. 61-291545, examples in Japanese Patent Application Laid-Open No. 62-277345).
However, these reaction systems are basically batch system or switchover system. Because there is the limitation in the improvement of the reaction rate through catalyst development for such a transesterification reaction, and the reaction rate is still slow, and thus it has been thought that a batch system is preferable to a continuous system. Of these, a continuous stirring tank reactor (CSTR) system in which a distillation column is provided on top of a reactor has been proposed as a continuous system, but there are problems such as the reaction rate being slow, and a gas-liquid interface in the reactor being small, based on the volume of the liquid. Hence it is not possible to make the conversion high. Accordingly, it is difficult to attain the object of producing the aromatic carbonate continuously in large amounts stably for a prolonged period of time by means of the above-mentioned methods, and many issues remain to be resolved before economical industrial implementation is possible.
The present inventors have developed reactive distillation methods in which such a transesterification reaction is carried out in a continuous multi-stage distillation column simultaneously with separation by distillation, and have been the first in the world to disclose that such a reactive distillation system is useful for such a transesterification reaction, for example a reactive distillation method in which a dialkyl carbonate and an aromatic hydroxy compound are continuously fed into a multi-stage distillation column, and the reaction is carried out continuously inside the column in which a catalyst is present, while continuously withdrawing a low boiling point component containing an alcohol produced as a by-product by distillation and continuously withdrawing a component containing a produced alkyl aryl carbonate from a lower portion of the column (see Patent Document 13: Japanese Patent Application Laid-Open No. 3-291257), a reactive distillation method in which an alkyl aryl carbonate is continuously fed into the multi-stage distillation column, and the reaction is carried out continuously inside the column in which a catalyst is present, while continuously withdrawing by distillation a low boiling point component containing a dialkyl carbonate produced as a by-product and continuously withdrawing a component containing a produced diaryl carbonate from a lower portion of the column (see Patent Document 14: Japanese Patent Application Laid-Open No. 4-9358), a reactive distillation method in which these reactions are carried out using two continuous multi-stage distillation columns, and hence a diaryl carbonate is produced continuously while efficiently recycling a dialkyl carbonate produced as a by-product (see Patent Document 15: Japanese Patent Application Laid-Open No. 4-211038), and a reactive distillation method in which a dialkyl carbonate and an aromatic hydroxy compound or the like are continuously fed into the multi-stage distillation column, and a liquid that flows down through the column is withdrawn from a side outlet provided at an intermediate stage and/or a lowermost stage of the distillation column, and is introduced into a reactor provided outside the distillation column so as to bring about reaction, and is then introduced back in through a circulating inlet provided at a stage above the stage where the outlet is provided, whereby reaction is carried out in both the reactor and the distillation column (see Patent Documents 16: Japanese Patent Application Laid-Open No. 4-224547, Japanese Patent Application Laid-Open No. 4-230242, Japanese Patent Application Laid-Open No. 4-235951).
These reactive distillation methods proposed by the present inventors are the first to enable aromatic carbonates to be produced continuously and efficiently, and many similar reactive distillation systems based on the above disclosures have been proposed thereafter (see Patent Documents 17 to 32: Patent Document 17: International Publication No. 00/18720 (corresponding to U.S. Pat. No. 5,362,901), Patent Document 18: Italian Patent No. 01255746, Patent Document 19: Japanese Patent Application Laid-Open No. 6-9506 (corresponding to European Patent No. 0560159, and U.S. Pat. No. 5,282,965), Patent Document 20: Japanese Patent Application Laid-Open No. 6-41022 (corresponding to European Patent No. 0572870, and U.S. Pat. No. 5,362,901), Patent Documents 21: Japanese Patent Application Laid-Open No. 6-157424 (corresponding to European Patent No. 0582931, and U.S. Pat. No. 5,334,742), Japanese Patent Application Laid-Open No. 6-184058 (corresponding to European Patent No. 0582930, and U.S. Pat. No. 5,344,954), Patent Document 22: Japanese Patent Application Laid-Open No. 7-304713, Patent Document 23: Japanese Patent Application Laid-Open No. 9-40616, Patent Document 24: Japanese Patent Application Laid-Open No. 9-59225, Patent Document 25: Japanese Patent Application Laid-Open No. 9-110805, Patent Document 26: Japanese Patent Application Laid-Open No. 9-165357, Patent Document 27: Japanese Patent Application Laid-Open No. 9-173819, Patent Documents 28: Japanese Patent Application Laid-Open No. 9-176094, Japanese Patent Application Laid-Open No. 2000-191596, Japanese Patent Application Laid-Open No. 2000-191597, Patent Document 29: Japanese Patent Application Laid-Open No. 9-194436 (corresponding to European Patent No. 0785184, and U.S. Pat. No. 5,705,673), Patent Document 30: International Publication No. 00/18720 (corresponding to U.S. Pat. No. 6,093,842), Patent Documents 31: Japanese Patent Application Laid-Open No. 2001-64234, Japanese Patent Application Laid-Open No. 2001-64235, Patent Document 32: International Publication No. 02/40439 (corresponding to U.S. Pat. Nos. 6,596,894, 6,596,895, and 6,600,061)).
Among reactive distillation systems, the present applicants have further proposed, as a method that enables highly pure aromatic carbonates to be produced stably for a prolonged period of time without a large amount of a catalyst being required, a method in which high boiling point material containing a catalyst component is reacted with an active substance and then separated off, and the catalyst component is recycled (see Patent Documents 31: Japanese Patent Application Laid-Open No. 2001-64234, Japanese Patent Application Laid-Open No. 2001-64235), and a method carried out while keeping a weight ratio of a polyhydric aromatic hydroxy compound in the reaction system to a catalyst metal at not more than 2.0 (see Patent Document 32: International Publication No. 02/40439 (corresponding to U.S. Pat. Nos. 6,596,894, 6,596,895, and 6,600,061)). Furthermore, the present inventors have proposed a method in which 70 to 99% by weight of phenol produced as a by-product in a polymerization process is used as a starting material, and diphenyl carbonate can be produced by means of the reactive distillation method. This diphenyl carbonate can be used as the raw material for polymerization of aromatic polycarbonates (see Patent Document 33: International Publication No. 97/11049 (corresponding to European Patent No. 0855384, and U.S. Pat. No. 5,872,275)).
However, in all of these prior art documents in which the production of aromatic carbonates using the reactive distillation method is proposed, there is no disclosure whatsoever of a specific process or apparatus enabling mass production on an industrial scale (e.g. not less than 1 ton per hour), nor is there any description suggesting such a process or apparatus. For example, the descriptions regarding the heights (H1 and H2, respectively: cm), the diameters (D1 and D2, respectively: cm), the numbers of stages (n1 and n2, respectively) of the pair of reactive distillation columns and the feeding rates of the raw material (Q1 and Q2, respectively: kg/hr) disclosed for producing diphenyl carbonate (DPC) from dimethyl carbonate and phenol are as summarized in the following table.
TABLE 1PATENTDOCU-H1D1n1Q1H2D2n2Q2MENT600252066600252023153502.8—0.23055~1015+0.621PACK-ING5005500.64008500.6231004—1.42004—0.8243005401.5—5250.72812002040866002520313334600—2066600—202235See Patent Document 34: Japanese Patent Application Laid-Open No. 11-92429 (corresponding to European Patent No. 1016648, and U.S. Pat. No. 6,262,210 See Patent document 35: Japanese Patent Application Laid-Open No. 9-255772 (corresponding to European Patent No. 0892001, and U.S. Pat. No. 5,747,609)
In other words, a pair of the biggest continuous multi-stage distillation columns used when carrying out this reaction using the reactive distillation system are those disclosed by the present applicants in Patent Documents 33 and 34. As can be seen from Table 1, the maximum values of the various conditions for the continuous multi-stage distillation columns disclosed for the above reaction are H1=1200 cm, H2=600 cm, D1=20 cm, D2=25 cm, n1=n2=50 (Patent Document 23), Q1=86 kg/hr, and Q2=31 kg/hr, and the amount of diphenyl carbonate produced has not exceeded approximately 6.7 kg/hr, which is not an amount produced on an industrial scale.